Radio receiving system



Jan. 9; 1940. J. D. REID RADIO RECEIVING SYSTEM riginal Filed sept. so, 19:55

W. n I

amusent on.

IN V EN TOR.

Patented Jan. x9, 19x40 f *Y i y.

UNITED STATES: PATENT oFFic-E",

John D. Reid," Philadelphia, Pa., assigner to Radio Corporation cf America, a corporation of Dela-y Ware y Original application Septenfxberv 3 0, 1935, Serial w No. 42,903.' Divided and this `applicationl f February 26, 1938, Serial No. 192,703

4 claims. `(Cl. 25o-:cm

' My invention relates to a radio receiving sysf part of my invention, per se. These several eletem. More specifically, my invention relates to ments are well kknown to those skilled in the art asimplifled all-wave superheterodyne receiver and do not require detailed illustration. in' which the rst detector and local oscillator In thev accompanying schematic diagram an "5 maybefcombined in a multi-purpose thermionic antenna I is connected tothe primary 3cr a radio '-55 tube. The application is a division of'. my cofrequency transformer 5. rIrne inductance'of the pending application Serial No. 42,903,1iled Sepprimary `is preferably chosen lso that, with the -tember30, 1935, granted May 10, 1938 as Patent antennacapacity and its own'inherent capacity, No. 2,116,713. f j it will resonate within the tuning range ofthe :W The development of the circuits .for Jsupe'rmiddle frequency band of the receiver. Onthe heterodyne radio receivers has been progressing rst or lowest frequency band,ia capacitor 'land towardr simplicity of parts and Wiring; The use resistor 9 are serially connected across the pri- .of higher frequencies for'broadcast transmission mary.r The capacitor lowers the resonant.fre. rf has brought about the designy of many all-Wave fluency 0f the primary t0 a Value Within the 10W' 1* receivers. These vreceivers are characterized lby est frequehy bal-'1d 0f the TeCeiVer- A SSISS Cil*- 15 a plurality of tuning inductors and capacitors cuit H, resonant to the frequency of the 'which require most complicated switching means intermediate frequency amplifier, fis shunted with resulting'complication of wiring.v `Thus no across the Primary to' attenuate voltagesof insmall part of the approach to a simplified superterfering signals. 'I K f 20 heterodynehas been lost in the development vof The secondary ofv the radio frequency trans- 1,.; the all-Wave receiver.` former is composed ofthree windings 'I3, I5, il Receiver development has ybeen accompanied which; are used respectively in the high, medium by improvements'in thermionic tubes. Thetubes and 10W fl'flileci band Ofthe receiver. "Phe have, for example, been simplied by theV inclulst vand' 58601101 O these Windings i3, ll5 are 2'5 sion and combination of several electrodes ina mutually COllpledtO thpimaly 3f I Single envelop to serve several functions." These A Singlesestn, three DOStOIlVIange sWtCh 5% tubes are called multi-purpose tubes, k Altrloiugrl isconnected to selectively-'choosethe desired opthe multi-purpose tube has decided benets 'at erating range. In this switch Contact arms 20 move `over a groundedcommutator 22. In this vlow frequency, difliculties have' been experienced r3.0 'at' the higher frequencies. I propose'to overcome Switch the first three contacts iS, '2I, 23 are these and other difficulties by the present'inven? COIlIlCBd t0 'the'M0159? induCtOfS and Cap'atYS tionwhich may be best understood. by reference for 'the 10W. medium. and high frequency ranges.

to the-'accompanying drawingl and specification The' first contact I9 connects the capacitor 'l and one of the objects of my invention Vis found resistor 9 across the` urrrlarv. The capacity '435 in the rsimplified means v`for selectively choosing tunes the PlmalyvtO a lil-8011161105 Within the 10W 'any one'fof a plurality of frequency ranges.vv range. `The resistor Il damrens the primary cir-y Another object is the method of avoiding the cuit and prevents undesirable reactions with the degenerative effects of a combined first detector tuned secondary `ClCllll The Secondary, CTUit and local oscillator tube. on the low range lis composedfof the three sec- 40 l0 "A further object is in the means employed Ondary windings,l I3, I5, il, which are serially to avoid fluttering or overall audio feedback, and connected, a trimmer capacitor 24- across the ripple effects which are troublesome in superthird of these windin'g'sgand a variable' capacitor heterodyne circuits. 25 which has a parallel' connected trimmer ca- A still further object is the method of coupling pacitor 2l. One. side of the variable capacitor 45 K "I5 the antenna system to the all-Wave receiver em- 25 is grounded and the other side connected to i Vbodying my invention. the free end of secondary winding I3; the free Additional objects will be found in the accorm end of the third secondary winding Il is panying'specification; grounded, and thusone side of the low-range sec- In the accompanying drawing is. shown a scheondary circuit is grounded, Af thermionic radio t50 matic diagram olf one embodimenty of my invenfrequency amplifier '29' isV 'connected across the 50 ytion applied to an all-wave superheterodyne secondary circuit by a 'blocking capacitor 3|, ATheintermediate frequency amplier, the second which connects the high potential terminal of detector and autcmaticvolume control, the audio theA secondary circuit to the control grid 33, frequency amplifier, the loudspeaker, and the and bythe grounded cathode of the amplifier 65 :power source .oi rectied, .lter current are not 29. The control grid isbiased by a directcurrent 55 is shunted across they third winding, 55.

potential derived from the automatic volume control rectifier.

The medium frequency range is chosen by placing the range switch on the second contact 2|. In this position the range switch discon nects the capacitor 'l which shunts the primary. The effect of removing this capacity is to tune the antenna or primary circuit within the range of the medium range. The third secondary Wind-u ing I1 is short-circuited and grounded. The secondary inductance is composed of the firs:J and secondary windings i3, l5. The tuning capacitance is made up of the variable capacitei- 25 and the trimmer capacitor 21p.

The high frequency range is chosen by moving: the range switch to the third contact 23. ln this position the antenna or primary circuit is t tuned to a frequency lower than the lowest fre quency within the high frequency range. rIhe secondary circuit is composed of the first secondary winding I3 which is connected to ground through a tracking capacitor 35. The function of th-e tracking capacitor will be described below.

`The reactance of the remaining secondary windings I5, ll' is negative' at the high frequencies of this range and its effect is lto increase the capacity of the tracking capacitor.

The output circuit of the radio frequency ani-- plier is of the low impedance type. rEhe anode circuit within the tube is made of low impedance by joining the screen el-ectrode 5l to the anode 39. The anode is connected to the prin-lary `li of a radio frequency transformer The primary is also connected to the positive terminal 42 of the B vcltage source |21. The inductance of the primary is chosen so that with its associated capacity it will resonate at a frequency just below the lowest frequency of the high frequency range. A damping resistor l5 is shunted across the primary to avoid pronounced resonance peaks.

On the low frequency range the range selector switch is positioned on terminal 55 which is grounded by arm 28 so that the primary il is effectively shunted by a` capacitor El and a resistor 9. The combined effect of these elements is to tune the primary to a frequency within the lowest frequency range and further damp its resonant peak. The secondary of the transformer i3 is made up of three secondary windings 5|, 53, 55 which are serially conducted. The rst two windings 5l, 53 are mutually coupled to the primary. A trimmer capacity 5l The tuning is accomplished by a variable capacitor '5S which is shiuited by a trimmer capacitor 5 E. The variable capacitor is grounded.

The high potential terminal of the secondary circuit is connected to the control grid 53 of the first detector and local oscillator tube 65 through a capacitor Gland a series resistor 5S. The junction between the capacitor and t.-e series resistor 5S is connected through'a grid resistor 'il to the negative terminal of the automatic volume control means. The output circuit comprises the anode 13, a resonant circuit 'i5 tuned to .the intermediate frequency, and a connection to the posi- 55 is short-circuited by the range switch arm 20 which grounds terminal 25. 'I'he secondary inductance in the medium range is composed of the first and second windings 5|, 53. The adjustable tuning capacity is made up of the inherent capacities of the circuit and the variable capacitor 58 with its trimmer G l. The secondary circuit is .coupled to the first detector and mixing tube S5 minal`28. The secondary circuit of transformer l 43 is tuned by the variablecapacitor 59 and the inherent capacities associated with the circuit.

The local oscillator is comprised of a cathode Tl, grid 79, and anode 8| which electrodes are included within the envelop of the first detector 65. The cathode is grounded.- The grid is connected through a grid capacitor 53 to the highpotential terminal of a variable capacitor which is shunted by a trimmer capacitor 81 and gro-unded. The grid is connected to a grid leak resistor 89 which is grounded.

Three inductors 9|, l93, 95 comprise the in-` ductance of the grid circuit. Of these inductors, the high potential terminal of the first induotor 9| is connected to the variable capacitor 85. The low potential terminal of the first induotor 9| is connected by means of a commutator 9'! to an insulated movable blade 99 of the range switch l5. The second inductor 53 has its low potential terminal grounded and its high potential terminal connected to the contact 46 of the range switch. The third induotor has its high potential terminal connected to the range switch contact 44. A trimmer capacitor lli! connects from. the high potential terminal of this induotor 95 to ground. The low potential terminal of the third induotor 95 is connected to ground by tive terminal 42 vof the B Voltage source |27 through a radio frequency choke |09and afilter network H5, Ill which will be described below. This induotor G5 is' also mutually coupled to the first grid circuit induotor 9| and through a blocking capacitor to the second anode induotor lill. The second anode induotor |01 is connected through the tracking capacitor |53 to ground. This common capacity |03 connection is also the feedback connection for the low frequency range of the oscillator. is mutually coupled to the second grid circuit induotor 93 for feedback at the medium frequency range.

On the low frequency range the grid circuit of the oscillator is. tuned to the signal frequency plus the intermediate frequency, which may be 450 kilocycles by way of example. The grid cir- The second anode induotor |01 cuit is' comprised of the first and third inductors 9|, 95, shunt trimmer capacitors 8l, IGI, the Variable capacitor 85, and the series tracking capacitor 03, The feedback is primarily through the tracking capacitor H33 which is common to the grid and anode circuits. This common capacitor |53 increases the effective coupling as the frequency is decreased. The anode circuit is composed of thetwo anode vcircuit-inductorsA |05, |01 which are connectedlby the blocking capacitor l| The mutual coupling between the rstI grid inductor 9| and the first `anode inductor |05 tends to increase thefeedback at the higher yoscillator frequencies. "|01 increases the load inthe vanode circuit.

The oscillator for the medium orrniddle frequency'range has a grid circuit which is composed of the first' and second grid inductors 9|,

53 and the variable and vxed capacitors 85, 81. v-Th'eanode'circuit is composed of the two anode inductors |05, Iii?. The second of these inductors is mutually coupled to the second grid in- Aductor 93. lIt will be observed that the usual 'tracking capacitor is omitted. Theomission of 'the tracking capacitor is possible because the eifectof the radio frequency primary 4|, which is tuned 'within the medium range, is to gradually decrease the resonant frequency of the detector inputl circuit as it is tuned to higher fre- Y'tracking may be obtained without the use of series tracking capacitors. The omission of series capacitors permits a wide frequency rangey to be covered. The oscillator per se is made to oscillate at a frequency `equal to the signal frequency plus the intermediate frequency. In this medium frequency range the third gridinductor 95 'of the oscillator is short-circuited, by the connection ofA terminal 36 and arm E0 of range switch |23, to avoid undesired reactions.

It will be observed that the oscillator for the low and middle frequency ranges has been adjusted to operate at frequencies which are higher than the signal frequency by the amount of the intermediate frequency. It has been the practice by those skilled in the art to follow the samey practice at the'higher frequency ranges, for example, above six megacycles. Where the first detector and oscillator tubes are combined in a single envelope, the oscillator reacts in an antiregenerative sense on the first detector when the oscillator frequency is higher than the detector frequency. This anti-regenerative effect or degeneration is probably due to some inherent capacity couplingorthelike between the oscillator electrodes and the control grid electrode. In the presence of such capacity, if the oscillator circuit is tuned to a higher frequency than the signal, the control grid circuit will be a capacitive reactance and produce degenerative effects.

I have found that these effects, which greatly attenuate the incoming signal may not only be avoided but the incoming signal may be greatly amplified by making the control grid circuit inductive with respect to the tuned oscillator circuit. This is the proper condition for regenerative rather than degenerative effects Under some conditions the first detector may tend to oscillate at the higher frequencies. A relatively low value of resistance serially connected to the control grid will overcome this tendency and still preserve the signal amplication.

The second anodeinductor The vinductive"v effect is`l broughty about by the simple expedient lf tuning'the oscillator to a frequency equal" ltothe signal frequency minus theintermediate frequency in the high frequency range.

inductor `9|,`the trimmer lcapacitor l81, and the variable capacitor? 85. The anode circuit is composed ofthe first anode'inductor |05 which is -mutuallyfc'ou'pledtothe first grid inductor. The

junction between the blocking capacitor and second anode inductor |01 is grounded in this range-by the range switch I8. i

Since the oscillator frequency'on the high frequncy 'range is maintained at a constantfreque'ncyv below the radio frequency and detector vinput circuits, no series tracking capacitor is used vinthe oscillator. In place of the usual oscillator tracking capacitor, a series" tracking `capacitor 35 is employed in the radio' frequency input circuit. This capacitor keeps the radio frequency input circuit'atthe required constant vfrequency above the oscillator frequency. A

series tracking capacitor is not'required in the detector input circuit because of the effect of the Y primary 4|. This primary is resonant below the lowv frequency end of the high frequency range, and as'its resonant frequency is approached, the primary reduces the rate of change of frequency of the 'detector input circuit. AThis effect is equivalent to the series tracking capacitor 35 in the radio `frequency input circuit and is used to make the several circuits track properly.

Itqshould be noted that the oscillator anode 'and screen grid are both connected to the same lvpositive terminal of the power supply. The voltage to the screen grid is reduced by a series resistor H3. A second series resistor ||5 and grounded capacitor ||1 act as an effective audio frequency filter. v `source varies, the filter will greatly attenuate If the potential of the positive these variations which become most serious on the high frequency ranges. Moreover, the oscillator anode andthe screen grid haveopposing effects which tend to neutralize the effect of voltage variations vand thereby prevent power supply ripple or flutter.v The term flutter is used to describe overall audio frequency fluctuations which are fed from. the audio amplifier to fhe oscillator and repeated through the system. Because of the excellent filtering and comparative freedom of the oscillator anode and oscillator screen potential from audio frequency variations, I have found that this terminal ||8 is a suitable junction for anode potential' of the first audio amplifier.

In the diagram I have omitted a detailed showing of the heater circuits, and the automatic volume control circuits. These connections are indicated but are not completed. This omission simplifies the diagram. The output of the first detector and local oscillator may be fed to an intermediate frequency amplifier H9, and hence to a second detector and A. V. C. circuit |2|. The output of the second detector may be ampliiied by an audio amplifier |23 .and reprolduced by a loudspeaker |25. A power source |21 for the system may be batteries, alternating current, which may be rectied and filtered, or the like `I have mentioned the terms high, medium or middle, and low frequency ranges, which may cover, respectively, the following ranges: 6 to 18 megecycles, 1.6 to 6 megacycles and 540 to 1000 kilocycles. e

It should be noted that the variable capacitors The grid circuit of the oscillator in the high frequency range is composed of the first grid 25, 59, 85 are connected to a single control. Each of these variable capacitors is shunted by trimmer capacitors which align the tunable circuits in the high and medium frequency ranges. The us-e of a single trimmer for the two ranges is effected by choosing inductors which are carefully held to the proper Values of inductance and distributed capacity. Additional trimmer capacitors are preferred in the low range as it would be dicult and expensive to manufacture the inductors of larger value to the eXactness required if trimmers were to be omitted.

I have described a radio receiving system which eifectively covers three ranges of frequencies, and in which the antenna is effectively coupled on all frequency ranges. The oscillator has been made to overcome serious degenerative effects substituting a regenerative gain for the degenerative loss. The circuit connections and filter arrangements prevent iiuttering. Numerous modications within the scope of my invention will occur to those skilled in the art. It should be understood that I do not intend to limit my invention except as required by the prior art and the appended claims.

I claim as my invention:

l. In a device of the character described, a local oscillator including a thermionic tube having cathode, grid, oscillator anode, control grid, screen grid and anode electrodes; an intermediate amplifier, a detector and an audio amplifier; a source of power subject to variations initiated through said ampliers by a change in the frequency of said oscillator, connections from said sourcejto said local oscillator and said` intermediate and said audio amplifiers; a filter for audio fr-equency currents connected between said source of power and said oscillator anode and screen grid electrodes, so that oscillations due to the effect of changing frequency on the source of power and the source or power on the frequency re prevented.

2. In a superheterodyne receiver, a thermionic local oscillator having cathode, oscillator anode,

and screen grid electrodes, an audio amplifier, a source of direct current potential subject to load variations, connections from said source to said audio amplier, connections including a common resistor from said oscillator anode and said screen grid electrodes to said source, a capacitor eiectively connected across said resistor whereby variations in said source potential initiated by changes in said oscillator frequency cause variations in screen grid current through said common resistor which tend to oppose changes in potential on said oscillator anode, and thus to oppose said frequency change 3. In a superheterodyne receiver, a thermionic local oscillator having cathode, oscillator anode and screen grid electrodes, a radio frequency amplier tube having a screen grid electrode, a source of direct current potential subject to load variations, connections including a first and a second resistor between said source and said oscillator and amplifier screen grid electrodes, connections including said rst resistor between said oscillator anode electrode and said source, and a capacitor effectively connected across said first resistor, whereby variations in said source potential cause variations in the total screen grid current through said common resistor which tend to oppose changes in potential on said oscillator anode.

4. In a superheterodyne receiver having a local oscillator which employs a screen grid electrode, the method of reducing flutter which is caused by the reaction of changing direct current potentials on the frequency of said local oscillator which includes the steps of ltering the direct current potential to partially remove said variations, and applying a compensating potential to said screen grid electrode Whose reaction on the frequency of said oscillator is equal in degree but opposite in sense to they normal reaction of said frequency to changes in said direct current'l potential. i, 1 i 'l JOHN D. REID. 

